THERMOSETTING ACRYLIC RESINS

which is superior to either alkyd- melamine system. Enamel from Resin C is about equal to the coconut alkyd- melamine enamel in impact resistance but is much harder and, in general, has better resistance properties then either alkyd finish. I t is more resistant to stains and detergents than the enamel from Resin B, but does not equal the flexibility of the former. Both experi- mental enamels are significantly harder and more resistant than the enamel from Resin A previously cited.

Enamel from Resin B has also been compared to the two conventional alkyd appliance whites in overbake color and gloss retention and shows definite su- periority when overbaking for 1 hour at 350” F. The superiority becomes even more marked when testing 1 hour a i 450’ F.

1

The usefulness of the acrylamide in- terpolymers as sole resins in enamels, and when modified with epoxy resin has been illustrated. The following is an example using Resin B with a vinyl chloride copolymer resin (Vinylite VM- CH).

Parts by Weight

Titanium dioxide 155.0 Resin B solution 433.7 Xylol 23.3 Vinylite VMCH solution (25% 373.0

Solids in 1 to 1 isophorone and methyl isobutyl ketone)

This composition calculates to be 70Yo by weight acrylamide interpolymer and 3oY0 by weight vinyl copolymer. An enamel film baked 30 minutes at 300O F. is thermoset, highly adhesive to steel,

Parts

Resin C 90 75 50

by Weight Bake 0.5% HaPOa Impact Epoxidieeda Temp., Sward Resistance,

Oil Minutes O F. Hardness Inch-Pound 10 30 300 44 25 30 300 42 50 30 300 Soft

2 48 48

a Epoxidieed oil was Admex 710.

Epoxy Resins in Thermosetting Acrylics

T H E COATINGS INDUSTRY has experi- enced several recent trends which have encouraged investigation of thermoset- ting acrylic resins. Some of these im- portant trends are:

Naturally occurring polymers and oils continue to give way to “custom- built” polymers synthesized from pure, highly reactive monomers and inter- mediates.

e As a result of the raw material sup- pliers’ very large-scale production eco- nomics, synthetic resins and monomers continue their almost yearly downward shift in prices but upward improvement in purity.

0There is a constant trend away from large quantities of volatile, hazard- ous solvents. Synthetic latexes, water- soluble vehicles, high solids, one-coat enamels, and solventless coatings are the results.

0 In the finishing industry, an im- portant factor is the further expansion of techniques and materials for coating metals prior to fabrication, so that appli- cation and curing conditions can be better controlled.

0 To be consistent with these develop- ments, polymer chemistry is offered new challenges. Now, relatively low molecular weight reactive polymer

tinplate, and aluminum foil, tough, and flexible. The film is resistant to alkali, acid, and solvents such as alcohols, aromatic naphthas, and ketones.

The compatibility of epoxidized oils with acrylamide interpolymer resins was previously mentioned. Resin C is one of the hardest, least flexible inter- polymer compositions. The following shows the plasticizing effect of epoxidized oil interblending testing as clear films.

With 10% epoxidized oil, there is little or no reduction in the hardness of the film over using the straight interpolymer resin, whereas there is slight improvement in impact resistance. Other features such as light stability of the film would be improved by the addition of the epoxi- dized oil. When 25Y0 to 50% epoxidized oil is used there is a marked improvement in the flexibility of films.

From these comparative properties the general adaptability of acrylamide interpolymer resins for industrial finish- ing has been briefly indicated.

H. A. V O G E L and H. G. BITTLE

Pittsburgh Plate Glass Co. Research and Development Center Paint Division Springdale, Pa.

“building blocks” are needed. Tradi- A review of the Chemical Abstracts tionally, a great Portion of Polymer patent literature up to April 10, 1960 synthesis has been directed toward gives the unlimited number of different

weight without cross linking. In the newer industrial coatings and plastics cross linkers adaptable to thermosetting chemistry, the molecular weight build- up is done by our through For our initial studies, our interest was cross linking [‘in situ” after the material narrowed to the more recent solvent- is applied. borne thermosetting resin art which in-

achieving highest possible molecular polymer building blocks and coreactive

Reactive lnterpolymer Patents Group I Group I1

Hydroxyl- N-Methylol- functional functional

U. S. 2557266 U. S. 2681897 U. S. 2853462 Belg. 554183 U. S. 2853463 Can. 573728

U. S. 28701 16 U. S. 2870117

{iiitT*;:7y7Y8 U. S. 2897174 U. S. 2900359 Brit. 590035

Group I11 Carboxyl- functional

u. s. 2324739 E;!: ;::;;; U. S. 2604464

Can. 491115 Can. 534002 U. S. 2662870 Can. 534001 JU. S. 2798861 \Can. 534261 U. S. 2810706 Can. 569430

1 {

Group IV Epoxide- functional

u. s. 2524432 U. S. 2580901 U. S. 2687405 U. S. 2692876 U. S. 2723971

U. S. 2729625 U. S. 2849418 u. s. 2857354 U. S. 2868760

Group V

Miso. U. S. 2604463 Brit. 681031

U. S. 2866767 U. S. 2899404

Can. 567165 Brit. 482897

VOL. 53, NO. 6 JUNE 1961 463

Epoxy Resins Studied

Designation

Experimental I

Experimental I1

Experimental I11

D.E.R.b 332

D.E.R.b 337 D.E.R.h 661 D.E.R.b 664

D.E.NaC 438

Epoxol7-4d EP 20P

Idealized Structure 0 / \ c-c-c-0-c-c-0-c-c-0-c-c-c

~

C I

C 0

Epoxide

Weight“ 260 c. Equivalent Viscosity, Color

Gardner

197 52 cps. < 1

0 / \ / \ c-c-c-0-c-c-0-c-c-0-c-c-0-c-c-c

I CCl

1 CCl

1 CCI

0 /O\ r , 1 / \ c-c-c-0 -c-c-0- c-c-0

L 6 -17 0 C 0

c-c--c-0- / \ c>-$-c)-.-c-c-c / \

C Bisphenol A-epichlorohydrin Bisphenal A-epichlorohydrin Bisphenol A-epichlorohydrin

Epoxidized soybean oil /~\-

\‘/v .<I c ~ ,>o

210 100 cps. < 1

335 88 cps. < 1

175 5000 cps. < 1 (liquid form)

257 Semisolid 3 525 Solid, M.P. 77’ C. < l 950 Solid, M.P. 99O C. 3

0

-c-c / \

180 Semisolid 5

220 Paste < 1 82 Solid, M.P. 184’ C. 3

a Grams of resin containing one gram-equivalent of epoxide. D.E.R., trade mark of The Dow Chemical Co. for its Bisphenol A-epichlorohydrin e Source, Union Carbide epoxy resins.

Chemicals Go. D.E.N., trade-mark of The Dow Chemical Co. for its epoxy novolac resins. Source, Swift & Co.

volves the following polymer com- ponents:

Relatively low molecular weight (monomer-free) linear polymer chains, each of which consists essentially of

A major portion of low-cost vinyl mmomer plus,

Generally a lesser amount of an acrylate ester, and

A small amount of a third poly- merizable monomer having a second reactive site not affected by the vinyl polvmerization.

Polyfunctional intermediates which will coreact with the relatively low molec- ular weight linear polymer chains, causing cross linking during the heat-curing step after application.

A list of selected patents pertaining to thermosetting acrylic resins is given (p. 463). These patents have been grouped according to the pendant reac- tive sites along the polymer chain. The “acrylic” nature varies from almost all acrylic ester content to almost all polystyrene because our primary con- cern is with the pendant reactive sites and the use of polyepoxides as cross- linking additives.

1.

2.

3.

This list of selected patents should only stimulate further thinking about epoxide resins as “curing agents” for other poly- mers. This study on the effects of epox- ide structures on some film properties of cured thermosetting acrylic systems was obtained on three unlike but repre- sentative interpolymers. The purpose was to compare epoxide resins in the Same thermosetting mechanism. The significant nature of the interpolymers we synthesized is described in the following list.

Carboxyl “Polymer A.” A resin synthesized by conventional polymeriza- tion of unsaturated monomers and suffi- cient amount of an acrylic acid to give 0.174 carboxylic acid equivalent per 100 grams of resin (described in U. S. Patents 2,798,861; 2,604,464; and others).

N-Methylol “Polymer B.” A resin synthesized by conventional polymeriza- tion of unsaturated monomers including approximately 15 % by weight of formal- dehyde derivative of acrylamide and a small amount of a polymerizable acid to act as a curing catalyst (described in U. S. Patents 2,870,116; 2,870,117; and others).

Commercial Thermosetting Acrylic Acryloid AT-50, This product was used as supplied by Rohm & Haas Co.

Ten different epoxy resins were selected for this work. Included were experimental epoxides which are color- less, have uerj low viscosity, and are non- phenolic.

Four of the series represent variations in the molecular weight of the standard bisphenol A-epichlorohydrin series.

D.E.N. 438 epoxy novolac resin was of interest because it contains more than three epoxy groups per average molecule, has fairly high molecular weight, yet is soluble in aromatic solvents.

Epoxidized soybean oil was also in- vestigated as was dicylopentadiene di- epoxide.

Conclusions

Many different acrylic interpolymers can be thermoset by using many types of epoxy resins. Properties are just as dependent on the choice of epoxy system as they are on the choice of acrylic inter- polymer.

464 INDUSTRIAL AND ENGINEERING CHEMISTRY

T H E R M O S E T T I N G A C R Y L I C R E S I N S

The epoxy-cured acrylic systems are characterized by very good adhesion, solvent resistance, and resistance to salt fog corrosion. All coatings studied thus far required a baking schedule to attain full cure.

Phenolic-derived epoxy resins co- reacted with acrylics show the expected excellent chemical resistance but are prone to yellowing discoloration from

ultraviolet light. Because of their high inherent viscosity, they also require considerable solvent in coatings formu- lations.

The experimental aliphatic liquid epoxy resins as cross-linking additives for acrylics provide films which have good solvent resistance. Initial studies show these films to differ markedly from similar ones made with conventional

epoxies by having much improved re- sistance to ultraviolet light, and by requiring lesser amounts of solvent, and in some cases by providing more flexibility.

D. D. APPLEGATH

The Dow Chemical Co. Midland, Mich.

Thermosetting Compositions Based on Acidic Copolymers Cross-linked with Diepoxides

D U R I N G a study of the reactions of polyepoxides, it was found that vinyl- cyclohexene dioxide could be poly- merized, by means of acid catalysts, to viscous sirups. The sirups could be applied to various substrates and further polymerized to tough, thermoset coat- ings. Part of the study of the reactions of various polyepoxides involved their use as cross-linking agents for other polymers containing groups which undergo addition reactions with poly- epoxides. A later program included a wide variety of polymers containing various reactive functional groups cross- linked by other polyfunctional materials. A particularly interesting case was one in which one polymer contained two types of groups-for example, a co- polymer containing both acrylic acid and glycidyl acrylate (4). This article gives an account of the development of one coat, universal appliance finishes based on acidic copolymers cross-linked with diepoxides.

Experimental Work and Discussions As might be expected, early experi-

ments showed that copolymers high in

styrene content were preferred for re- sistance to grease, chemicals, and de- tergent solutions. Furthermore, of all the systems studied, the acid copolymer- polyepoxide system catalyzed by base was the best for performance on unprimed metal and was also preferred in that the temperature and time required for cross linking were within the range used in the appliance industry. The epoxy resins were soon restricted to the condensation products of diphenylolpropane and epi- chlorhydrin. Thus copolymers con- taining styrene, an acrylate or meth- acrylate ester, and acrylic or methacrylic acid received the most attention and the copolymers were cross-linked with the bisphenol type of diepoxide.

If all the monomers and initiators were premixed and added over a time interval to refluxing solvent, the acrylic acid was found to be poorly distributed in the copolymer. By adding the acrylic acid separately, and in such a way as to give a low initial concentration in the reaction mixture and a steadily increasing concentration as the reaction proceeded, a copolymer of uniform acrylic acid distribution was obtained.

::E .4 11 -I

.3 I- 4 .*t 1 .I 1 I I I I I I I I I I I I 1 1 I I I I I l I l0,OOo rm,ooo

L O G M,

Figure 1. intrinsic viscosity expression

Light scattering measurements were used to obtain K and

As might be expected, it was not simply the acrylic acid content which was important for adequate cross linking but the average number of carboxyl groups per polymer molecule. I t was desirable to increase the molecular weight to as high a value as possible and a relationship between intrinsic viscosity and weight average molecular weight was found. The methyl esters, prepared by reaction with diazomethane. were used rather than the free acids (Figure 1). From this plot was obtained the expression

1 ~ 3 = 1.59 x 1 0 - 3 ~ 0 . 4 2 A copolymer which yielded enamels of good application properties and which when cross-linked had good film prop- erties had a molecular weight of about 30,000 and 25 carboxyl groups per mole. Between one half and one equivalent of epoxide resin was used.

As reported by Schecter and Wynstra (3), the reaction between carboxyl and epoxide is base catalyzed. Inorganic bases, amines, quaternary ammonium compounds, and copolymerized basic

Enamel Properties Copolymer

Vinyltoluene 72 % Ethyl acrylate 20% Acrylic acid 8%

Diepoxide Epon 828 Gloss 93 at 60D Adhesion to Bonderite Excellent

Adhesion to Alodized Excellent 1000

AI Flexibility Grease resistance (15

days at 60° C. in 1 :1 cottonseed oil :oleic acid)

Detergent resistance (2% Tide at SOo C.)

Heat resistance

in the Pencil hardness

Fair Unaffected

One coat (1.5 mils), 200 hrs.

Two coats (2.2 mils), 1000 hrs.

6 hrs. at 315' F. to cause notice- able change

3H

VOL. 53, NO. 6 JUNE 1961 465